The precision of a calibre depends upon the quality of its regulating member, and very high oscillation frequencies, for example of 10 Hz, compared to the usual frequencies of 2.5 to 4 Hz, are only obtainable if suitable regulating members are devised, in particular as regards the balance.
Indeed, the energy to be provided for maintaining oscillation, in the form of elastic balance spring torque, is proportional to the product, on the one hand, of the inertia of the balance about the pivoting axis, and, on the other hand, of the square of the frequency. Thus, for example, for the same energy, a frequency change from 4 Hz to 10 Hz results in the inertia being divided by approximately 6. For a frequency of 4 Hz, a balance inertia of 12 mg/cm2 is considered to be good, since this type of balance conventionally has a diameter of 9 to 10 mm. Thus, a balance for use at 10 Hz must have a low inertia value, in particular less than 2 mg/cm2.
For optimum operation, a balance for use at 10 Hz must also have minimal mass, notably less than 30 mg, so as to reduce friction in the bearings, to avoid isochronism disturbance in the various positions of use.
Although it has low mass and inertia, the balance of a high frequency oscillator must also allow adjustment of the unbalance and perfect poising, both static and dynamic, and the construction thereof must make setting and/or adjustment operations possible. It is not therefore possible to use conventional technology, or solutions with lighter balances such as the balances wherein the felloe has spokes (?) disclosed in FR Patent No. 1275 357 in the name of Straumann, or FR Patent No. 1 301 938 in the name of LIP. Indeed, even the reduced mass of these balances does not provide sufficiently low inertia. Likewise, the mass and inertia of a titanium balance in accordance with EP Patent No. 1 562 087, in the name of MONTRES BREGUET SA and devised with a titanium felloe and arms and reduced sections, are still greater than required for optimum operation.
A Q factor on the order of 500 is also sought, thus considerably higher than that of conventional oscillators where, for good quality watches, the Q factor is close to 220 to 280. This Q factor can only be obtained by combining a silicon or similar balance spring with a balance that satisfies the above conditions. In addition to obtaining a high Q factor, combined with setting and adjustment possibilities, the index-assembly must also be omitted.
Moreover, since the mass of the unit is limited, the smallest possible number of components should be preferred.
However, micro-machinable materials, such as silicon and quartz, which are theoretically made in finite dimensions, with very precise tolerances, in their development method, are not easy to machine subsequently.
Various documents describing improvements made to balances are known. CH Patent Application No. 343,904A, in the name of ROLEX MONTRES, discloses a balance felloe comprising an elastic holding means, in the form of a slot, locking an insert formed by an inertia-block pin. WO Patent Application No. 2008/080570 A2, in the name of COMPLITIME SA, discloses inertia-blocks provided with slots for a friction fit. EP Patent Application No. 1,351,103 A1, in the name of CHOPARD MANUFACTURE SA, discloses elastic U-shaped inertia-blocks inserted into recesses in the felloe via elastic deformation. CH Patent Application No. 345,600 A, in the name of ROLEX WATCHES, discloses a slit sleeve for holding and elastically gripping an inertia-block. CH Patent Application No. 261,431 A, in the name of PATEK PHILIPPE, discloses adjustment weights centred on studs and immobilised by their own elasticity. CH Patent Application No. 89,273 A, in the name of PAUL DITISHEIM, discloses non-protruding filler weights held by their own elasticity on walls of a cavity which may or may not be threaded. CH Patent Application No. 280,067 A, in the name of PATEK PHILIPPE, presents adjustment weights elastically mounted on a stud, whose centre of gravity is off-centre relative to said stud.
It is therefore necessary, for regulating members made of such materials or incorporating at least one component made of this type of material, to have the possibility of frequency and/or inertia adjustments, but by avoiding machining and by prioritising setting possibilities.